Acoustic barrier device for suppressing detonation waves in piston engine combustion chambers



july 22, 1969 A. G. BOBINE 3,456,638

ACOUSTIC BARRIER DEVICE FOR SUPPRESSING DETONATION WAVES IN PISTON ENGINE COMBUSTION CHAMBERS 2 Sheets-Sheet 1 Filed Jan. Ales, 196e 1N WJJNT'OR. I EQT 6. oDlNE july 22, 1969 A. G. BoDlN: 3,456,638

ACOUSTIC BARRIER DEVICE FOP( S J SI DETONATION WAVES IN PISTON ENGINE CO ON AMB INVENTOR. ALBERT 6. Bouma U.S. Cl. 123-191 8 Claims ABSTRACT OF THE DISCLOSURE An acoustic barrier member is located in a combustion chamber in close proximity to the wall of the chamber. Apertures in said barrier member are dimensioned so that in cooperation with the narrow space between the barrier member and the chamber wall they form efficient acoustic attenuators at the detonation frequencies, thereby effectively suppressing the detonation gas vibrations.

This invention relates to internal combustion piston engines and more particularly to an attenuator device for suppressing the detonation waves generated in this type of engine.

The device of this invention is an improvement in the eld covered by my Patent No. 2,573,536, issued Oct. 30, 1951, entitled, Engine Detonation Control by Acoustic Methods and Apparatus, and others of my patents including No. 2,662,516 issued Dec. 15, 1953, No. 2,712,816 issued July l2, 1955, No. 2,760,472 :issued Aug. 28, 1956, and No. 2,828,731 issued Apr. l, 1958.

These prior patents all describe techniques and apparatus for suppressing the vibrations generated in internal combustion engines, to counteract `the undesirable effects such detonation vibrations produce. My aforementioned Patent No. 2,573,536 particularly provides a thorough teaching of the overall problems involved and the theoretical consideration in suppressing the detenation in suppressing the detonation vibrations by acoustic techniques. These teachings are hereby incorporated in this application by reference and will be referred to periodically, as the description proceeds.

The improvement of this invention is based on several significant factors discovered with regard to the detonation vibrations or waves generated in internal combustion engine combustion chambers. First, the more significant gas vibrations contributing to the detonation react to the dominant dimensional environment which is usually somewhat in the form of a iiat cylinder or pancake shape, this being the dominant configuration of the combustion chamber usually formed at the beginning of the stroke cycle when the detonation waves are generated. In this type of pancake shaped chamber, most of the acoustic energy is `developed across a plane normal to the longitudinal axis 4of the cylinder, with the gases vibrating back and forth transversely between the cylinder walls in what are known as sloshing modes. In this .thermoacoustic performance, there is an acoustic high frequency pulse comprised of many acoustic sloshing cycles reiiecting across the chamber during the very short time interval to the beginning of each stroke cycle. In other words, the gases tend to vibrate more vigorously across the large flat dimensions of the pancake than they do up and down through the short thickness dimension near top dead center. This is because the acoustic interaction with combustion favors the lower acoustic frequency of the sloshing modes.

Since piston engines are basically comprised of cylinder and pistons, the combustion chamber, no matter what the detailed contour thereof, also tends to be of cylindrical nited States Patent O 3,456,638 Patented July 22, 1969 conformation. This is especially true of the shape of `the combustion space after top dead center, where the piston has moved down a bit as it has when detonation normally takes place. In other words, no matter what is the contour of the combustion chamber ceiling, or inside of the cylinder head, the general character of piston engine combustion chambers is flat, shallow, cylindrical Wafer, sometimes refered to as a pancake shape. The thickness of this pancake shape is inversely proportional to the engine compression ratio. In many engines this pancake shape tends to -be wedge-shaped; that is thicker along one portion of the periphery, and thinner along a remaining portion. However, as mentioned above, these complexities lose their importance as soon as the piston has moved down somewhat from the cylinder head, so that the inherent cylindricity begins to emerge.

It is particularly true, I have yfound that the longer acoustic wavelengths of the lower frequency gas vibrations are not too conscious of cylinder head details, such as hemispherical type, wedge type, slant type, quench type, step type, etc., which are now popular. A dimensional characteristic has to be large relative to a Wavelength, in order for the sound wave to take much notice and be peculiarly reflected thereby.

Accordingly, this invention is first addressed to the discovery that the more important gas vibrations tend to behave as if the space were a flat cylinder. The next part of the discovery is that most of the acoustic energy is in the long wavelength sloshing modes wherein the gases vibrate back and forth along some direction in a plane which is normal to the axis of the engine cylinder. In other words, the gases vibrate more vigorously across the large flat dimension of the pancake than they do up and down through the short thickness dimension.

Recognizing these very significant factors, the device of this invention provides an acoustical barrier member which is designed to provide high attenuation at the deternation vibration frequencies, such barrier member being placed directly between the central portions of the pancake combustion chamber and the wall of said chamber so that it receives the full onslaught of the detonation waves. Further, the barrier member is located near the rim of the pancake but spaced a short distance from a combustion chamber wall so that there is a small volume between the barrier and the wall of the combustion chamber. The barrier member has apertures formed therein which are dimensioned in conjunction with the space provided between the barrier and the cylinder wall to provide maximum attenuation at the detonation frequencies. Further, the barrier is given a height which spans the thickness dimension of the pancake so that it effectively blocks the path between the central portion of the combustion chamber and the chamber wall, thereby efficiently acting upon all of the acoustical energy in the transverse vibration modes. Thus, the barrier member with its plurality of apertures, dimensioned so as to provide acoustical attenuation at the detonation frequencies, effectively dissipates the detonation energy and dampens the vibrations to the point where they are no longer of appreciable significance.

Certain embodiments of this invention have a further advantage over prior art devices in that the `barrier is located in the main combustion space of the associated comlbustion chamber and is made an integral part of the engine, being located in the cylinder wall, the cylinder head or the piston. The barrier is thus intimately involved in each combustion cycle of the engine and does not provide an unwanted hot spot which could unduly accelerate combustion; nor does it function as a side pocket or antichamber to undesirably trap burned gases and thus interfere with combustion chamber sequencing.

The devices of this invention thus provide acoustic barrier means which extends around a periphery of the pancake formed by the combustion chamber in proximity to the wall of such chamber which is in the direct path of the predominant modes of the detonation waves so that in cooperation with the space found between it and the wall, it efiiciently dissipates the energy of such waves.

In working with the devices shown in my above mentioned prior patents, I have discovered that frequently each detonation acoustic pulse is initiated during combustion by a sharp, high energy pressure versus time spike which initially echoes around the chamber and causes a lot of undesirable engine roughness, and noise. The devices of this invention operate on the initial onslaught of this rst spike and the ensuing vibrations.

Briefly, the devices of the invention comprise a barrier member which runs along a substantial portion of the wall of the combustion chamber in spaced relationship thereto. This barrier member is located along the uppermost portion of the combustion chamber walls to form a barrier between said walls and the central portion of the combustion chamber in the initial por-tions of the stroke cycle when the detonation waves are generated. The barrier member has a plurality of apertures extending therethrough, each of said apertures operating in conjunction with a space between it and a chamber wall to form an attenuation unit at the frequencies of the significant detonation waves. These apertures in certain embodiments are in the form of elongated slots, and in others, in the form of cylindrical channels. By electrical analogy these apertures are equivalent to resistances in parallel. The barrier member may be formed at the top of the piston, the walls of the cylinder head, or a combination of the WO.

It is therefore a principal object of this invention to provide a more eicient device for attenuating the detonation Waves generated in an internal combustion engine.

It is a further object of this invention to provide a detonation Wave attenuator which is located right within the combustion chamber and in direct initial communication with the significant modes of the detonation waves.

It is still another object of this invention to provide a a barrier type acoustical attenuator which is integrally formed with the components of the engine in which it operates.

Other objects of this invention will be apparent from the following description taken in connection with the accompanying drawings, of which:

FIG. 1 is an elevation view of a first embodiment of the device of the invention,

FIG. 2 is a cross-sectional View taken along the plane indicated by 2-2 in FIG. 1,

FIG. 3 is an enlarged elevational view illustrating the barrier device of the embodiment of FIG. 1,

FIG. 4 is an elevational view in cross-section of a second embodiment of the device of the invention,

FIG. 5 is a cross-sectional view taken along the plane indicated by 5 5 in FIG. 4,

FIG. 6 is an elevational view in cross-section of a third embodiment of the device of the invention,

FIG. 7 is a cross-sectional view taken along the plane indicated by 7-7 in FIG. 6,

FIG. 8 is an elevational view in cross-section of a fourth embodiment of the device of the invention,

FIG. 9 is a cross-sectional view taken along the plane indicated by 9--9 in FIG. 8, and

FIG. l0 is an elevational view in cross-section of a fifth embodiment of the device of the invention.

Referring now to FIGS. 1-3, a first embodiment of the device of the invention is illustrated. Cylinder 11 has a piston 12 slidably mounted therein which is driven by the combustion gases generated by virtue of the ignition provided by spark plug 14 and in conjunction with the synchronous operation of valves 15 and 16. The device thus far described is nothing more than a conventional `internal combustion engine. The invention is concerned with acoustic barrier member 17 which is integral with the top of piston 12 and runs around the periphery of the piston. Barrier member 17 may be machined in the top of the piston or may be separately fabricated and welded to the top of the piston. Barrier member 17 is located proximate to the Wall of cylinder head 20, a cavity 18 being formed between the cylinder head wall and the barrier member. Barrier member 17 has a plurality of slotted portions 21 formed therein, and extending around the entire extent thereof. Slots 21 are made to have dimensions such as to form cavities in conjunction with the width of space 18 which at the frequency of the significant detonation frequencies provide wave traps or attenuators. Thus, they effectively dissipate the detonation energy. The techniques by which such detonation frequencies can be determined and the significant considerations in determining the dimensions of the attenuation slots are fully discussed in my aforementioned Patent No. 2,573,536, and therefore need not be repeated herein. It should be noted, however, that in this particular instance, the combined dimensions of both slots 21 and space 18 must be considered in the design.

In the operation of the device of the invention, the detonation waves are generated immediately after ignition when piston 12 is in the approximate position indicated in the figure. As already noted, the combustion chamber at this time is somewhat in the form of a pancake with the significant detonation waves running in plane generally parallel to the surface of the pancake and normal to the longitudinal axis of the piston as indicated, for example, by arrow 19. These waves are effectively surrounded by barrier member 17 and therefore strike directly against this barrier as they travel towards the combustion chamber Wall. In view of the dimensional characteristics of the cavity attenuators formed by each of slot members 21 in conjunction with space 18, these waves are effectively absorbed so that there is little reliection back from the walls of the chamber and the detonation energy is substantially attenuated so that its deleterious effects are minimized.

This major dissipation of the onslaught of the wave as it strikes the perforated barrier is somewhat akin to the action of a breakwater which dissipates ocean storm wave energy. One further feature herein, is, of course, the frequency response characteristic which can be made effective in this invention by virtue of dimensional control as aforesaid.

Referring now to FIGS. 4 and 5, a second embodiment of the device of the invention is illustrated. As in the first embodiment, there is a barrier member 17a extending around the periphery of piston 12, this barrier having a plurality of slots 21 formed therein. Circurnferentially surrounding this barrier is space 18 which corresponds to the space provided in the first embodiment. This embodiment differs from the first embodiment in that it additionally has a barrier portion 17b which is formed in the `wall of the cylinder head and is staggered outwardly of barrier portion 17a in concentric relation thereto. Barrier portion 17b is generally similar to barrier 17a and has slots 21 formed therein which can be generally aligned with corresponding slots formed in barrier portion 17a. As for the first embodiment, these various slots as related dimensionally with the space 18 provide high attenuation at the detonation frequencies to effectively dissipate the detonation energy.

Referring now to FIGS. 6 and 7, a third embodiment of the device of the envention is illustrated. In this embodiment, the acoustic barrier 17 is formed around the periphery of the top portion of piston 12, and in this instance the apertures 21, rather than being in the form of slots are in the form of holes or cylindrical channels extending through the barrier. As in the other embodiments, space 18 circumferentially surrounds the barrier. Holes 21 are dimensioned with the same general considerations as for the corresponding slots in the other embodiments to provide the cooperation with space 18 high attenuation to the detonation frequencies.

Referring to FIGS. 8 and 9, a further embodiment of the device of the invention is shown. In this embodiment, the barrier member is comprised by `barrier portion 17b having slots 21 therein and formed in the cylinder head, and drilled portion 17a having holes 21 formed therein, located around the periphery of piston 12, the apertures 21 operating in conjunction with space 18 to form the' attenuator elements.

Referring now to FIG. 10, a further embodiment of the device of the invention is illustrated. In this embodiment, the barrier 17 is formed in the top of piston 12 by virtue of a groove 18 machined in the top of the cylinder, this groove providing the required space surrounding the barrier. The dimensions of slots 21 are designed in conjunction with those of groove 18 in the same fashion as for the other embodiments to provide the desired attenuation characteristics. This form is particularly suited to diesel engines; and in such usage spark plug 14 is replaced by a fuel injector.

Thus, all of the various embodiments of the invention have in common a barrier member which is located near the periphery of the combustion chamber positioned in the direct path of the detonation waves and formingv an effective boundary 'between the central portion of Vthe combustion chamber and the Walls of said chamber. The barriers in each of the embodiments have apertures therein which are dimensoned in conjunction with a space surrounding the barrier and located between it and the cornbustion chamber wall which provides high attenuation at the frequencies of the detonation waves. In this manner, the direct onslaught of the detonation waves is intercepted by the barrier and dissipated to the extent where such detonation waves are reduced to minor proportions.

I claim:

1. In an internal combustion engine having at least one cylinder forming a combustion chamber and a piston slidably mounted in said cylinder, the improvement comprising acoustic barrier means for attenuating detonation vibrations generated in said chamber,

said barrier means being located in said chamber between the central portion thereof and the chamber wall in direct communication with said central portion,

a space being formed in said chamber surrounding said barrier means and in external concentricity therewith, .l

said barrier means having a plurality of apertures formed therethrough, said apertures and said space forming acoustic attenuator means dimensioned to dissipate sonic energy at the frequencies of said detonation vibrations.

2. The combustion engine of claim 1 wherein said acoustic barrier means forms a ring running around the top of said piston near the periphery thereof, said space being formed between said barrier means and the Wall of said chamber.

3. The engine of claim 1 wherein said acoustic barrier means forms a ring running around the top of said piston, said space being formed by a groove in the top of said piston, said groove surrounding said barrier means.

4. The engine of claim 2 wherein the apertures are'in the form of slots formed around substantially the entire extent of said ring.

5. The engine of claim 2 wherein the apertures are in the form of holes formed around substantially the entire extent of said ring.

6. The engine of claim 1 wherein said barrier means comprises a first barrier member formed around the periphery of said cylinder and a second barrier member formed around the periphery of said piston.

7. The engine of claim 1 wherein said barrier means comprises a slotted ring shaped member formed around the periphery of said cylinder.

8. The engine of claim 7 lwherein said Ibarrier means additionally includes an apertured rim portion of said piston extending around the periphery of said piston.

References Cited UNITED STATES PATENTS 2,738,781 3/1956 Bodine 12S-191 2,739,583 3/1956 Bodine 123-191 2,752,907 7/1956 Bodine 123-191 2,752,908 7/ 1956 Bodine 123-191 2,760,473 8/1956 Bodine 123-191 2,827,033 3/ 1958 Bodine 123.-191

WENDELL E. BURNS, Primary Examiner 

